Extraction of copper from comminuted mineral mixtures.



UNITED I STATES ERNEST A. LE SUEUR,

Patented March 22, 1904:

PATENT OFFICE.

OF OTTAWA, CANADA.

EXTRACTION OF COPPER FROM COMMINUTED MIN ERALMIXTURES.

SPECIFICATION forming part of Letters Patent No. 755,302, dated March22, 1904.

A lication filed May 27, 1899. Serial No. 718,486; (N 0 specimens.)

To all whom} it may concern; I

Be it known that I, ERNEST A. LE SU UR, a subject of the King of GreatBritain, residing at Ottawa, in the county of Carleton, ProvinceofOntario, Canada, have invented certain new and usefulImprovements in theExtraction of Copper fromComminuted Mineral Mixtures, of which thefollowing is a specification.

My invention consists in treating said material with an ammoniacalsolution containing a. reagent or mixture of reagents capable ofoxidizing copper. While it has long been known that a water solution ofammonia will dissolve copper oxid and while it is comparatively easy todissolve copper scrap, filings, or turnings, &c., by treating them witha solution of ammonia exposed to the air and to consequent oxidation,the present problem is a very different one.

What I propose to treat by myprocess is not a mass of metallic copper,but a mixture containing a very small percentage (in point of factusually less than one per cent.) of that metal. The consequence is thatthe (compara tively) little copper there is is, so to speak, buried outof sight in the mass of sands or mud inclosing it, and as oxidation ofthe copper before it can go into solution is essential it is a hopelesstask to attempt to secure such solution by merely exposing to the air amass of this mixture submerged in ammonia. In this latter case thecopper in the very top layer of the mudwill be oxidized and go intosolution; but that is all. r

So far as I know my method of introducing an oxidizing agent into thesolution and leaching or otherwise treating the mixture with saidsolution is absolutely novel. With reference now to the reagent orreagents to be used to effect oxidation of the copper it is the casethat certain cupric compounds (I prefer the hydroxid) in solution inammonia or its carbonate will slowly give up a portion of their oxygento the metallic copper. The solution that I prefer, however, depends forits usefulness on the remarkable fact which I have discoveredthat anammoniacal solution of cupric hydroxid, for instance, hasits oxidizingpowers extraordinarily enhanced by theaddition of certain apparentlyinert salts Y of ammonia. Thesalts I prefer for this purpose are thesulfate and nitrate, and when a small quantity of either or bothof theseis added to the above-mentioned solution the rapidity with which saidsolution attacks finely-divided copper is extraordinary. For instance,in making experiments on certain of the waste sands from the stamp-millsof the Calumet & Hecla Mining Co. I have" found half of the total coppergo into solution in less than eight minutes. I may here point out thatthe use of ammoniumchlorid is objectionable on account of the danger(should electrolytic extraction be adopted) of formation of thefearfully dangerous compound, nitrogen chlorid. i

' The solution may be allowed to act either with or without access ofair, or it may be allowed to act with a certain amount, althoughinsuflicient to fully oxidize the extracted cop per of such access. Ifthe solution is exposed to the air at intervals during the working ofthe method, the oxygen which was abstracted from it to oxidize intosolution the desired copper will be replaced by the oxygen of the air.If, on the other. hand, no access of air be permitted, the solution willbe deoxidized' (in the .case of the above-described solution so as tocontain cuprous instead of cupric compounds) and the copper going intosolution will do so to the cuprous form. The disadvantage ofthis way ofpracticing the method is that it is necessary to carry in the solutionsufiicient oxidizing effect to take outthe whole of the copper to beextracted. On the other hand, using access of air we have the advantagethat as the copper increases in the solution in the cupric form theoxidizing power of the solution grows.

In working my process the reactions are as follows: To begin with thecomposition of my solvent solution may be stated thus:

In this formula, is greater than 2, and the ammonium sulfate may bereplaced by other salts of ammonium. As the solution grows older withrepeated use it may accumulate other inert matters in solution,depending on the particular method of precipitation of the copper whichis adopted. \Vhen this solution is applied to the copper in the wastesands above mentioned, the cupric hydroxid is reduced, sometimescompletely, to the cuprous form, as follows:

The ammonium sulfate appears to suffer no chemical change any more thandoes the ammonia itself; but the mixture of the two enables a very muchmore rapid solution of the copper to occur. than does even adecidedlystronger ammoniacal solution of cupric hydrate alone.

Having described the means of getting the copper into solution, I nowproceed to a discussion of the means of extracting it from saidsolution.

The extraction may proceed along either one of two general lines. Thefirst is electrical extraction, and the second is chemicalprecipitation. The particular method to be used depends, moreover, onwhether the copper is to be removed from the cuprous or the cupric form.

As regards electrical extraction, it will be observed that the problemis not what is usually the case in electrolyzing copper solutions'thatis to say, the result to be attained is not to remove copper from a moreor less impure anode and lay it down in a state of purity on a cathode;but what we require to do is to lay down upon the cathode the coppercontents (or a portion of them) of the solution itself. hat this amountsto is that we must either use an insoluble anode or else an anode theproducts of attack of which will not appear at the cathode and socontaminate the copper. Under the first head we may place the noblemetals, such as platinum, and in the second the only commerciallyavailable material is iron. In the use of iron anodes in this work thefollowing occurs: The iron is oxidized to the ferrous form, and as suchis soluble in the ammonia. The iron will not, however, make itsappearance at the cathode along with the copper so long as the latterremains in excess in the solution and the current density is not toohigh. Furthermore, I adopt the following expedient to remove the ironfrom the solution: I expose the solution to sufiicient access of air toconvert the ferrous iron to the ferric form. As soon as this happens theferric compound leaves the solution as an insoluble precipitate and isthereafter available as a pigment. A material for an anode whichoccupies a position midway between the two above-described classes iscarbon. On the one hand, it is more or less attacked by the action ofthe cell; but, on the other hand, the products are gaseous, and so donot require any further consideration.

Where it is practicable to do so, the most elegant method of working theprocess is to dissolve the copper without (or with but little) access ofair to the cuprous form, then to electrolyze with an insoluble anodeaway from the air until one-half of the copper has been removed. In thiscase no oxygen appears at the anode; but the nascent oxygen attacks thecuprous solutionto form cupric until just one-half of the copper insolution in the cuprous form at the commencement of electrolysisremains. The electrodecomposition of the cuprous compounds gives twicethe copper per unit of current that the electrolysis of cupric copperdoes, and at the moment that the reducing powers of the solution aresatisfied we arrive back at the point we started from as regards theamount of copper (cupric) held by the solution, and the latter is readyto be used over again. This statement is strictly true only where, onthe one hand, no wastes of solution occur, and, on the other, noatmospheric oxidation has occurred during the process. In practice thereis unavoidably a little of both, and these may be regulated so as tojust neutralize each other and keep the amount of cupric copper in thesolution at the end of any run constant.

Referring to the second general method of extracting the copperthat isto say, by chem-' ical precipitationthere is of course the obvious andwell-known means of throwing out the copper as sulfid. I prefer,however, to use the following: I add to the solution aquantity of thecheapest mineral acid locally producible or obtainable in quantity lessthan sufiicient to completely neutralize the ammonia. In this countrythe acid I prefer is the so-called chamber sulfuric acid. The effect ofsuch addition is to precipitate such of the copper (as was held insolution by that portion of the ammonia neutralized) in the form ofcopper hydroxid, or it may be basic or other carbonate. This precipitatecan be very readily removed from the solution by filtering or merely byallowing to settle. With a view to expedition I prefer the former. Theobject in leaving the ammonia in excess after the treatment is twofold.In the first place, as an acid reaction is avoided, the solution has noeffect (such as it would have if slightly acid) upon, for instance, aniron-containing tank. The chief reason, however, is to secure aretention by the solution of a certain amount of dissolved cupriccompound with a View to its oxidizing power on the next batch of onprousmaterial treated in accordance with whatI have above set forth.

The precipitate obtained as above is immediately available as a pigment.It may also be conveniently used as a basis for the manufacture at aminimum of expense of copper sulfate. Should, however,the object ofworking be the production of metallic copper, the said precipitate canbe smelted at a very low late in the solution the compounds resultingfrom the union of said acid and alkali. This, however, is usuallyunobjectionable.

The cheapest method known to me for the 7 preparation .of a solutionwhich will fulfil the purposes for which it is intended is to simplymake a mixture of ammonium sulfate and a suitable alkali in quantitysufiicient to liberate enough free ammonia or ammonium carcopper everytime, the labor and trouble would.

be many times what it is in this case, where a part only is extractedand the rest allowed to work around again.

I am aware that proposals have been put forward for the ammoniacalextraction of copper oxid from mixtures containing it, and the strikingfeature of difference between such proposals and my invention is that incarrying said proposals into operation the cupric contents of thesolution increase as solution proceeds, whereas in my process the saidcontents diminish as solution progresses.

What I claim is l. The method of dissolving metallic copper out ofmixtures containing it which consists in treating said mixtures withammoniacal solution containing a reagent or mixture of reagents capableof oxidizing copper, substantially as described.

2. The method of dissolving metallic copper out of mixtures containingit which consists in treating said mixtures with an ammoniacal solutioncontaining cupric compound or compounds, substantially as and for thepurposes set forth.,

3. The method of dissolving metallic copper out of mixtures containingit which consists in treating said mixtures with an ammoniacal solutioncontaining a cupric compound or compounds and a salt or salts ofammonia, substantially as set forth.

4. The method of obtaining metallic copper from mixtures containing itwhich consists, first in treating said mixtures with an ammoniacalsolution containing a cupric compound or compounds so as to dissolve thedesired copper, then in removing a portion of the total copper contentsof thesolution, and lastly in using the partially-exhausted solutionover again to dissolve fresh copper as before, substantially asdescribed.

In testimony whereof I afiix my signature in presence of two witnesses.

ERNEST A. LE SUEUR.

Witnesses:

. T. DARoY MGGEE,

W. S. EDWARDS.

